1. Field of the Invention
The present invention relates to a method for the preparation of polyether-ester elastomer and in particular, to a method for the production of polyether-ester elastomer having high cure rate, good melting viscosity and other excellent properties suitable for extrusion and blow moldings.
2. Description of the Prior Art
As known to those skilled in the art, thermoplastic polyether-ester elastomers are block copolymers wherein rubber-like polyether soft segments and plastic polyester hard segments are alternately linked to one another, so that they typically have excellent rubber-like properties such as low-temperature durability, flexibility, elastic recovery (elasticity) and etc., each caused by the soft segments, and excellent plastic properties such as mechanical strength, heat resistance, low-temperature resistance, moldability and the like, each caused by the hard segments. Such polyether-ester elastomers are thus useful for (flexible) hoses, belts, industrial elements, sport articles and etc.
However, it is known that these polyether-ester elastomers are not suited to a blow molding due to their low melt strength, furthermore, in case of high content of soft segments they have serious disadvantages in moldability caused by low cure rate thereof.
For solving these problems, there have been proposed several methods for improving the melt strength and the cure rate of the polyether-ester elastomer, for example, blending of butadiene/acrylonitrile, that is, nitrile rubber (NBR), a class of nitrile copolymers, with the elastomers, and addition of ethylene/methacrylic acid ionomer, a class of polymerized carboxylate, to the elastomers. However, these methods have a disadvantage in that, they cause occurrence of a phase separation in the elastomers during the molding method, while they efficiently improve the melt strength of the elastomers. In addition, aliphatic alkaline salts may be added to the elastomers to make them have improved melt strength and cure rate. However, this method is not preferred for practical use since it detrimentally affects the melt stability of the elastomers.
In another method, crosslinking of the elastomer may be achieved using primary amine or secondary amine as a crosslinking agent, thus improving the melt strength of the elastomers. However, this method shows a disadvantage in that it causes a problem in moldability of the elastomer because it reduces the cure rate of the elastomer.